Approach control apparatus for railway signaling systems



Sept. 12, 1939.

APPROACH CONTROL APPARATUS FOR RAILWAY SIGNALING SYSTEMS Filed July 26, 1938 2 Sheets-Sheet 1 V l 2J Sdy I 5e w Il@ 5?' I EL@ i l I 15 I E P 5 i 12T-[56; ,22 g 57 1l. 22% f 27 w .i-fzg AB g I7 f 5 .25 18 55 g I? I+ f L# F' [18T is, TAL-49 :I l f 2 I :5f T55 'i Rfk 5.9 I; V11:-

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"ir-fw 20T lNvENTQR 4. EdYap Thomas HIS ATTORNEY Sept. 12, 1939. E- Ul THOMAS 2,172,893

APPROACH CONTROL APPARATUS FOR RAILWAY SIGNALING SYSTEMS Filed July 26, 1938 2 Sheets-Sheet 2 17 l.; 17 Y h Egg. 7. ....9 wfgfzg. y.

y lNvENToR Edwad hama@ HS ATTORNEY Patented Sept. 12, 1939 UNITED STATES PATENT OFFICE APPROACH CONTROL APPARATUS FOR RAILWAY SIGNALING SYSTEMS Application July 26, 1938, Serial No. 221,317

25 Claims.

My invention relates to approach control apparatus for use in railway signaling systems of the coded track circuit class and it has special reference to the employment of such apparatus for approach controlling various signaling functions without the use of line wires.

Generally stated, the object of my invention is to improve certain features of an approach control without line wire scheme wherein the rails of each unoccupied `signal block length of track transmit code step pulses of auxiliary energy forwardly from the block entrance to ef fect the energization of a slow release approach relay at the block exit.

l5 A more specific object is to provide improved means for detecting these pulses at the exit end of the track circuit and for energizing the associated slow release approach relay in step with these pulses.

Another object is to prolong each period of this relay energization for the full duration of the signal code off period within which is occurs.

An additional object is to quicken the response of the approach relay to a shunting of the track circuit to such an extent thatcab signal flips at block joints will be avoided.

A further object is to detect the absence of received auxiliary energy within the space of a single code cycle. l

A still further object is to effect the above through the use of circuit means of comparatively simple character.

In practicing my invention I attain the above and other objects and advantages by introducing the pulses of auxiliary energy into the track circuit during the off periods of the main signal control code; by providing the exit end of the track circuit with a sensitive code following detector relay which receives these auxiliary energy w pulses from the trackrails and which causes the associated slow release approach relay to be energized in step with them; by providing the detector relay with a stick circuit which prolongs the hold-up time of that relay for the full duration of Aeach of the off periods of the signal control code within which that relay responds; and by supplying the approach relay with supplementary energizing pulses during the on code periods.

I shall describe a few forms of approach controlling apparatus embodying my invention and shall then point out the novel features thereof in claims. These illustrative embodiments are disclosed in the accompanying drawings, in

which:

Fig. 1 is a diagrammatic representation of a section of railway track which is equipped with one preferred form of my improved approach control apparatus;

Fig. 2 is a partial representation of the exit end facilities of Fig. l arranged in a slightly modified manner;

Fig. 3 is a code cycle diagram which is identified with Figs. 1 and 2;

Fig. 4 is a diagrammatic View of exit end fal@ cilities which employ a code following detector relay having but a single winding; and

Figs. 5 to 9 inclusive are similar showings of exit end facilities which use double winding detector relays and which supply the approach relays with supplementary energizing pulses during the on periods of the signal control code.

In the several views of the drawings, like reference characters designate corresponding parts. Referring first to Fig. l, the improved approach control apparatus of my invention is there disclosed in association with a coded track circuit system of automatic block signaling for a railway track I-Z over which it will be assumed that traflic moves in a single direction indicated 25 by the arrow, or from left to right in the diagram. The protected stretch of this track is divided into the customary successive sections by insulated rail joints 3 and the rails of each section form a part of a track circuit to which coded signal control energy is supplied in customary manner.

In Fig. 1, reference characters D and E respectively designate the entrance and exit ends of one of these track sections which is illustratively shown as being a full signal block in length; 35 character TR designates a code following track relay which is installed at the entrance end of the section and operated by energy received from the rails thereof; character 'IB a track battery or other direct current source provided at the'sec- 40 tion exit for the purpose of supplying these rails with the relay operating energy just referred to; character CR a coding device having a contact 5 which codes this energy by periodically interrupting the rail supply circuit; and character S 45 the usual wayside signal which guards the entrance of each of the track blocks and which is controlled by the associated track relay TR. through the medium of decoding apparatus I0.

The referred to coded track circuit system of 50 automatic block signaling operates without the aid of line wires and includes all of the elements above named. Further comprised by the system are the customary facilities (not shown) for continuously operating each of the exit end relays 55 of the wayside signal S at the same location.

CR at one or another of the usual plurality of distinctive code rates. In a typical three-indication system, two such rates are employed and ordinarily these will consist of '75 and 180 energy pulses per minute. Selection among the rates of signal control code is made in accordance with advance traffic conditions by the decoding apparatus l0 functioning in customary manner.

This decoding apparatus (details not shown) is controlled in the usual fashion by the associated track relay TR and it performs the further function of selectively setting up a lighting circuit for one or another of the lamps (G, Y `and R in the typical three-indication system above referred to) In the arrangement represented these signal lamps derive energizing current from a power source which is designated by the terminals plus and minus For applications in which train carried cab signals (not shown) also are to be controlled, the representative coded signaling facilities still further comprise means at the exit end of the track circuit for additionally supplying the rails thereof with coded alternating curr-ent energy. In the form shown at location E in Fig. 1, these means include a track transformer TT having a secondary winding which is connected with the track rails over coding contact 5 of device CR during each energy on period of the signal control code from battery TB. At proper times the primary winding of this transformer is energized over a conductor 'i from a suitable alternating current sourceV designated by the terminals B and C.

In order that certain functions of the signaling system may be rendered active only upon the approach of a train, the apparatus installed at each of the signal locations D, E etc. is supplemented by an approach relay AR which is arranged to maintain the referred to functions inactive at all times except when the section of track to the rear of the location becomes occupied. In the illustrative arrangement which is shown at location E in Fig. l., these approach con-- trolled functions consist in lighting the wayside signal S (normally dark) and in supplying the railsof the rack section to the rear of that signal with alternating current energy for cab signal control.

The former function is governed by a contact 9 of the approach relay AR and the latter by a cornpanion contact l i thereof. Either'of these functions may, of course, be controlled individually by the approach relay AR, and it will be apparent, moreover, that signaling functions other than or in addition to those just named may likewise be governed by the same relay.

When applied to coded signaling systems of the conventional character just considered, the improved approach control apparatus herein disclosed renders the relay AR at each signal location responsive to the approach of a train and does this, moreover, Without the use of control line wires.

For each of the signal blocks this approach control apparatus comprises: (l) entrance end facilities which supply the rails of that block with pulses of auxiliary energy which are in step with recurring periods of the signal control code; and (2) exit end facilities which receive these auxiliary pulses froml the rails and energize the approach relay AR in step with them.

In the form shown at location D in- Fig. 1, the entrance end facilities are the same as those disof the off code periods.

Transformer IRT is provided with a direct current exciting circuit which includes, in the particular form shown, a back contact I2 of relay TR and which is completed each time that the track relay releases. The resulting build-up of primary current causes the transformer to induce in its secondary winding a pulse of voltage (an equivalent effect may be produced by interrupting instead of completing the transformer exciting circuit upon each track relay release) having the polarity indicated by the vertical arrow. This is impressed upon the operating winding of the impulse relay IR and causes the relay to respond. The `relay IR is of the polar typey and contact i3 thereof occupies the lowermost position shown in full line as long as the relay remains deenergized or receives current of reverse relative polarity. In that position it connects the operating winding of the track relay TR directly across the track circuit rails l and 2.

When, however, relay IR receives from transformer IRT the beforementioned pulse of normal polarity energy it bias-es contact ES upwardly into the dotted position and thereby disconnects relay TR from the track rails and instead connects auxiliary battery AB thereacrcss. In this manner each release of the track relay TR causes the impulse relay IR momentarily to transfer the track rail connection from the winding of relay TR to the output circuit of battery AB. Due to the momentary character of the normal polarity output pulse from transformer IRT at the beginning of each of the off periods of the signal control codathe duration of each of these connection shifts is comparatively short.

In the form shown at location E in Fig. l, my improved exit end facilities comprise a detector relay KRL which responds to pulses of auxiliary energy received-over the rails l and 2 from battery AB,-.a.circut controlled by contact l 5 of that relay for locally energizing the approach relay AR from a source designated by the terminals plus and minus, means for making the relay AR Suniciently slow releasing to bridge the intervals between recurrent responses of the detector relay, and a stick circuit for the detector relay KR2 controlled over a contact i5 thereof and effective to prolong the hold-up time of the relay for the full duration of the off periods of the signal control code which coding contact 5 of device CR produces.

This detector relay KR?. is of the code following type and the represented interpostion thereof between the slow release approach relay AR and the track rails is similar to that disclosed and claimed in each of the following two copendirig applications: Serial No. 220,015 filed July 19, 1938, by Crawford E. Staples and Serial No. 223,076 led August 4, 1938, by Herman G. Blosser. In the form shown in Fig. l this detector relay is provided with separate pick-up and stick windings I1 and I8. The pick-up or operating windingll'l is connected in energy receiving relation with the track rails I and 2 only during the olf periods of the signal control code. This connection is completed by coding contact 5 when in its lowermost or released position. The stick winding I 8 of the relay KR2 isA energized from a suitable local source, designated by the terminals plus and minus, over a circuit which is set up by a second contact I9 of the coding relay CR (contacts 5 and I9 shift their positions simultaneously) and which is completed by the beforementioned front contact I6 ofthe detector relay KRZ.

The slow release approach relay AR may be energized in step with the responses of the detector relay KR2 in any suitable manner. As shown in Fig. 1, a transformer AT isV interposed between the winding of relay AR and a local source of direct current supply. The primary circuit of this transformer is pole changed by contact I5 of the detector relay in well-known manner and the output energy from the transformer is supplied to the operating winding of relay AR over circuits which include a rectifying contact ZI of detector relay. This particular arrangement of devices KRZ, AT and AR embodies principles that are disclosed and claimed in a copending applicationy Seral No. 210,744 filed May 28, 1938, by Frank I-I. Nicholson et al. As

shown in Fig. 2, a somewhat simpler though genl erally equivalent arrangement includes the contact I5 of the detector relay directly in the circuit of the operating winding for the approach relay AR. Both of these arrangements function to supply pulses of p-ick-up energy to the approach relay only when the d-etector relay KRZ is following code. s

In operation of the complete approach control system shown in Fig. 1, the track rails I and 2 of section D-E actin the usual manner to transmit energy from one end of the section to the other as long as the section remains unoccupied. Each time, under such conditions, that contact 5 of the coding device CR is inthe picked-up or on code periodV position the track battery TB picks up the track relay 'I'R over a circuit which may be traced from the positive terminal of the battery through a current limiting impedance`22, front contact 5 of device CR, conductor 23, track rail I, conductor 24, the Winding of relay TR,v conductor 25, back contact I3 of impulse relay IR, conductor 26, track rail 2, conductors `Z'Iand 28, the secondary winding of transformer 'TT and conductor 29 back to the negative terminal of the battery TB.

Each time that the coding contact 5 occupies the released or off code period position and connects the pick-up winding II of the detector relay KR2 across the track rails, the track relay TR at the entrance end ofthe section releases and contact I2 thereof completes for the transformer IRT the beforementioned exciting circuit which may be traced from the positive terminal of a suitable supply source through back contact I2, conductor 3| and the primary winding of the transformer back to the negative terminal of the supply source. This excitation induces in the secondary Winding of the transformer a pulse of normal polarity voltage which picks up the impulse relay IR over a circuit extending from the upper terminal of the transfdrmer secondary through conductor 32, the winding of relay IR, and conductor 33 back to the lower terminal of the transformer secondary.

This energization of relay IR occurs at the beginning of each of the ofi periods of the signal control code. In responding, contact I3 of relay IR momentarily picks up and disconnects the winding of `relay TR from the track rails and connects the auxiliary battery AB thereacross. Under this condition the battery picks up the detector relay KRZ at the exit end of the section over a circuit which may be traced from the positive terminal of battery AB through a current limiting impedance 35, front contact I3 of relay IR, conductor 26, track rail 2', conductor 2l, the winding I'I of relay KRZ, conductor 3B, back contact 5 of device CR, rconductor 23, track rail I, and conductors 24 and 31 back to the negative terminal of battery AB.

Under the influence of each of these auxiliary pulses of energy thus received from the trackway, the code following detector relay KRZ picks up and contact I5 thereof causes the operating winding of the approach relay ARto be supplied with a corresponding pulse of local pick-up energy. In addition, contact I6 of the detector relay completes the beforementioned stick circuit throughwhich winding I3 of the relay is energized until the end of the off period of the signal control code. In the form shown in Fig. l, this now completed stick circuit may be traced from the positive supply terminal through front y contact I6 of relay KR2, conductor 39, back contact I9 of device CR, and the relay winding I8 back to the negative supply terminal.

The resulting recurring pulses of local energization which are supplied over contact I5 of the detector relay to the slow release approach relay AR cause the approach relay to hold its contacts 9 and I I continuously picked up, thereby maintaining the wayside signal S and the track transformer TT at location E deenergized as long as the track section D-E remains vacant. They referred to slow releasing characteristic of relay AR may, of course, be imparted in any one of a number of well-known manners, such as by internal design expedients or the use of an external snubbing impedance (not shown).

Assume, now, that a train comes into the track section D- -E. The usual shunting action of its wheels and axles reduces to a Very low value the potential difference between the rails I and 2 and thus deprives both of the relaysTR and KR2 of pick-upy energy. Relay K RZ now remaining continuously released, the supply of local energization to the approach relay AR is discontinued. Inl consequence, that relay now completes at contacts 9 and I I the energizing circuits for signal Se and transformer TT at location E.

As a result the named wayside signal now lights the particular lamp selected by the decoding equipment I0 and the transformer TT supplies the rails of track section D-E with a pulse of alternating current energy from a source B-C each time that the contact 5 of device CR occupies its uppermost position. As has been mentioned, this energy is suitable for the control of cab signals which may be carried by the train proceeding through the track section and the circuit over which it` is supplied may be traced from the right terminal of the secondary winding of transformer 'IT through conductor 29, battery TB, impedance 22, front contact 5 of device CR, conductor 23, track rail I, the wheels and axles (now shown) of the train, rail 2 and conductors 2l and 28 back to the left terminal of the track transformer secondary.

In the particular form shown in Fig. l the primary circuit -for transformer IT is controlled by contactII of the approach relay AR in such manner that when therelay is releasedV the primary of the transformer is connected With the terminals B and C over back contact I |,'conductor 1 and conductor 40. When, however, the contact Il is picked up the connection just named is broken and the two terminals of the primary winding of transformer TT are bypassed over a circuit which extends from the right terminal thereof through conductor 4U, front contact Il and conductor l back to the left terminal. The purpose of this by-pass is to reduce the impedance which the secondary winding of the transformer presents to the flow of direct current from battery TB to the track rails under conditions of track section vacancy.

As soon as the rear of the departing train clears the exit end of location E the coded direct current energy from track battery TB is again transmitted by the rails to the track relay TR at the entrance location D That relay once more responds and the operation of contact I2 thereof causes the impulse relay IR again to connect the track rails in energy receiving relation with the auxiliary battery AB during each of the off code periods. These pulses of auX- iliary energy from battery AB are, in turn, transmitted by the rails to the detector relay KRZ at the exit location E. In responding to them that relay again causes the approach relay AR to receive recurrent pulses of local energizing current. Relay AR once more picks up and dueto its slow release characteristics continuously deenergizes the wayside signal Se and the track transformer 'II' at location E, thereby restoring both of these devices to their normally inactive states.

The approach control facilities shown in Fig. 1 are of particular advantage in coded signaling systems wherein train carried cab signals as Well as wayside signals S are to be controlled. In such cab signaling applications time or quickness of response by the slow release approach relay AR is an important factor, for when the cab signal energy is applied after the entrance of the train into the track circuit it is Adesirable that this energy be made available soon enough to avoid ilip or momentary false stop indications by the cab signals when the train vehicle on which they are carried passes over the insulated rail joints 3 at the track circuit entrance.

Generally speaking, the less the time that is required for introducing the alternating current cab signal control energy into the track circuit, the less will be 'the chance for this undesirable cab signal flip. Hence, detection of the entry of the train into the track circuit within the shortest time practicable is the operating condition most desired.

In an approach control without line wire scheme of the type shown in Fig. 1, however, the quickness with which this cab signal control energy may be applied to the track circuit following the entry of a train therein is, of course, limited by the release delay period of the approach relay AR. This period, in turn, can never be reduced beyond the time required to span the spacing between the recurring energy pulses which are locally supplied to the operating Winding thereof under the control of the code following detector relay KRZ.

The spacing between these recurring pulses is, of course, greatest for the lowest code which the signaling system employs for signal control purposes, and an approach relay AR which is sufficiently slow in releasing to remain continuously picked up when the `vacant track circuit is receiving this slowest code will operate properly for all other codes having a higher rate of energy pulse recurrence. Thus, in the case of the typical three-indication system assumed to employ two codes of 75 and 180 energy pulses per minute, the conditions present when the 75 code is being introduced into the track circuit are those whichY must be considered in xing the minimum period of delay release for the approach relay AR at the exit end of each track section.

It has been pointed out that the impulse relay 1R at the entrance end of the section picks up only momentarily at the beginning of each off period of the signal control code and thus causes the track circuit to receive a comparatively short pulseof auxiliary energy from the battery AB. Some idea of the comparative length of this pulse in relation to the cycle periods of the signal control code may be gained from an inspection of the diagram of Fig. 3.

In Fig. 3 the length of the auxiliary energy pulses is designated by the character 1c. This time corresponds to that during which the contact I3 of relay IR is picked up during each of the "off periods of the main signal control code supplied from battery TB over coding contact 5 of relay CR at the exit location E and responded to by the track relay TR at the entrance location D. When the highest speed code Which the signaling system employs consists of 180 energy pulses per minute as previously assumed, the time represented by k may be as small as (7100 second. This shortness is necessary to prevent overlapping of the auxiliary energy pulse (off code period) with adjacent "on periods of the named highest speed (180 or other) code of the signaling system.

To aid explanation, the diagram of Fig. 3 has been drawn on the basis of a signal control code having the assumed slower rate of '75 pulses per minute. Such a code is made up of recurring cycles each consisting of an oif period having a length of approximately second and an on period of about the same length. This means that each cycle of the 75 code has a total duration of of a second. These periods are substantially longer than those of the higher speed code of 180 energy pulses per minute, the cycles of which have a total length of 1A, second and the on and off periods of approximately 1/6 second each.

Were the detector relay KRZ at the exit location E to be operated solely by the auxiliary energy received over the rails I and 2 from the entrance end facilities, it would be necessary to design the approach relay AR for a release period of the order designated at b' in Fig. 3. For a signal control code of '75 energy pulses per minute this is only slightly less than second total cycle length. Assuming that the auxiliary energy pulse has a length of W second (the before stated value for lc of Fig. 3) the approach relay AR must be designed with a delay of not less than 74/109 second, and is preferably of the order of one full second to provide for proper operating margins.

This means that at least one second will elapse from the time that a train rst comes into section D-E until contact Il of the relay releases and supplies alternating current energy from source B-C to the rails over coding contact 5. Train carried cab signals of conventional design are found to display the "stop indication when the control energy therefor is interrupted for a period of this comparatively long character, and in this respect the assumed use of the auxiliary energy only to operate the detector relay KR2 produces a defective form of approach control operation.

In my improved exit end facilities which are represented at location El in Fig. l, this effect is overcome by providing the detector relay KRZ with the beforedescr-ibed stick circuit which prolongs the hold-up time of this relay for the full duration of the signal code off" period Within which the relay response occurs. The substantial order of this hold-up extension is indicated at c in Fig. 3. Instead of releasing at the end of the auxiliary energy pulse supplied over the track rails to the pick-up winding I1, the contacts of relay KRZ are maintained picked up by the stick winding I3 which continues to receive energy over front contact I6 and back contact I9 of code device CR, until the end of the off period, at which time the coding contact is moved to its uppermost position for producing another on code period.

This means that the periods of recurrent energization of the slow release approach relay AR are correspondingly extended to a value of the order indicated atY e in Fig. 3. When the relay employs the directly controlled energizing scheme shown in Fig. 2, the direct extension indicated in Fig. 3 applies. When the relay control scheme involves an interposed transformer of the character shown at AT in Fig. l, comparable improvements also are realized and in addition distorted on time operation of the coding device contacts, I5 and 2| is prevented from interfering with the desired continuous response of the approach relay.

In both cases the minimum period of release for the approach relay AR is reduced from value b to the much shorter time designated by character d in Fig. 3. For the 75 energy pulse per minute code, on the basis of which Fig. 3 has been drawn, it Will be seen that the reduced minimum delay period is only slightly greater than half as much as the minimum delay7 period when the detector relay KR2 is not provided with the stick circuit herein disclosed. In practical terms, this means that the approach relay AR no-w needs be designed to have a contact release period of only Ti, second as compared with the previous minimum of one full second or greater.

On the 180 or other higher energy pulse per minute code, the use of a detector relay KR2 having my improved stick circuit results in comparable reduction inthe spacing between consecutive pulses of energization which `contact I5 causes to be supplied to the operating Winding of the approach relay AR. For all codes, therefore, the effect is substantially to lengthen the periods of approach relay energization and to make possible the reproduction of very nearly equal on and 01T code step times (when device CR produces equal on and off. periods) of relay energization. As long as the initiating pulses of auxiliary energy from battery AB occur shortly after the release of the coding contact 5 of device CR this approximate equality will be maintained.

Although the initiating pulses may be of finite length (designated at lc in Fig. 3) the just stated relation will be maintained for each and every one of the different signal control codes (assumed to be of 75 and 180 energy pulses per minute for a three-indication system) Which the coded signalingsystem employs. Moreover, the nature of the stick circuit with which relay KR2 is provided is such that variations in the absolute length of these auxiliary energy pulses donot interfere with the operation justvdescribed.

Referring noW to Fig. 4 `I havethere represented a somewhat modified form of exit end facilities which correspond to those shown at location E in Fig. l. Structurally, the facilities of Fig. 4 differ from those of Fig. l in that use is made of a code following detector relay KR having but a single Winding which is arranged to perform both the pick-up and the stick functions.

As in the system of Fig. 1, the pick-up current is received from the entrance endfacilities (not shown in Fig. 4 but corresponding to those shown at location E in Fig. 1) over the rails I and 2 during the on periods of the signal control code which is produced by contact o-f the device CR. In Fig. 4, however, another contact :i2 (corresponding to I9 of Fig. l) is employed by the coding device and the track battery TB is employed as the source of stick current for the detector relay KR. This stick current is transmitted irom battery TB to the winding of detector relay KR whenever contact i6 of that relay is picked up at a time that contact 5 of device CR is in the lowerrnost or off code period position. Contact I5 of this detector relay controls the energizing circuit for the slow release approach relay AR in the same manner as shown in Fig. 2, that is, each time that relay KR picks up relay AR is energized over a circuit Which extends from the positive terminal of a suitable supply source through front contact I5 of relay KR, conductor 4I, and the operating winding of relay AR back to the negative terminal of the supply source.

In addition to controlling the circuit through which the before referred to stick current is transmitted, contact I6 of relay KR forms a part of the circuit over which pick-up current is supplied to the relay winding from the track rails. In the arrangement of Fig. 4, as in that of each of Figs. l and 2, the approach relay AR is provided with contacts 9 and II which control the wayside signal Se and the track transformer TT at location E in the manner previously explained in detail.

In operation of the approach control facilities i shown in Fig. 4, the track rails I and 2 of the section to the rear of location E act in the usual manner to transmit energy from one end of the section to the other as long as the section remains vacant. Each time, under such conditions, that the contacts of the coding device CR are in the uppermost position, the track battery TB supplies these rails with a pulse of track relay operating energy over a circuit which may be traced from the positive terminal of the battery through front contact 5 of relay CR, conductor 23, track rail I, the Winding of relay TR (not shown in Fig. 4), track rail 2, conductor 21, iront contact 42 of device CR, conductor 43, the secondary of track transformer TT, and current limiting impedance 22 back to the negative terminal of battery TB.

Each time that the Contact of coding device CR koccupies the lowermost position, the track relay TR (see location D of Fig. l) releases and causes impulse relay IR (again see Fig. l) to pick up its contact I3 and thereby momentarilyconnect the associated auxiliary battery AB with the track rails. Under this condition the winding of detector relay KR receives a pulse of auxiliary energy over a circuit which may be traced from thepositive terminal of battery AB (see Fig. l) through front contact I3 of relay IR, conductor 26, track rail 2, (see Fig. 4), conductor 21, back `contact 42 of device CR, conductor 45, the Winding of relay KR, conductor 45, back contact'l of relay KR, conductor 23, track rail i and ccnductors 2li and 3l (again see-Fig. l) back to the negative terminal of battery AB.

Under the influence of each of these auxiliary energy pulses, the code following detector relay KR picks up and thus completes the local enen gizing circuit for the slow release approach-relay AR at contact l5 and its own stick circuit at contact I6. This stick circuit may be traced from the positive terminal of track battery TB through back contact 5 of device CR, conductor 41, the winding of relay KR, conductor 5, front contact I6 of relay KR, and a current limiting impedance 4S back to the negative terminal or" battery TB. The intensity of the pickeup encrgization for the relay AR is so chosen 'that the relay armature moves the contact IG completely from the back to the front position due to the momentum which is produced by the initial surge of auxiliary trackway energy over the back contact I6.

As in the facilities of Fig. 1, the above traced stick circuit maintains the relay KR picked up until the circuit is broken by movement of con-- tact 5 of device CR to the uppermost position at the end of the off code' period. Thevcircuit, moreover, is so connected with battery TB that the polarity of energy which is supplied to its Winding KR is the same as that of the auxiliary energy received over the rails I and 2 from the entrance end facilities (not shown in Fig. 45)

Each time that contact I5 of relay KR is thus picked up, it completes for the approach relay AR an energizing circuit already described as including conductor 4I.

Under the influence of the recurring pulses of this energization this slow release relay AR holds its contacts 9 and II continuously picked up and thereby maintains the wayside signal S and the track transformer` TT at location E deenergized as long as the track section to the rear of that location remains vacant.

Assume now that a train comes into the track section just referred to. The usual shunting action of its wheels and axles reduces to a very low value the potential dilerence between the rails I and 2 and thus deprives the detector relay KR of pick-up energy. Now remaining continuously released, contact I5 of that relay continuously interrupts the energizing circuit for the slow release approach relay AR. That relay now releases and completes at contacts 9 and I I the energizing circuits for signal Sc and transformer TT.

In consequence, the named wayside signal lights the particular lamp selected by the decoding equipment and transformer TT supplies the track rails with pulses of alternating current energy from source B-C each time that the contacts of device CR occupy their uppermost positions. This cab signal control energy is supplied over a circuit which may be traced from the upper terminal of the secondary winding of transformer TI' through impedance 22, track battery TB, front contact 5 of device CR, conductor 23, track rail I, the wheels and axles (not shown) of the train, rail 2, conductor 21, front contact 42 of device CR, and conductor 43 back to the lower terminal of the transformer secondary.

As soon as the rear of the departing train clears the exit end of location E the coded energy from track battery TB is again transmitted by the rails to the track relay TR at the entrance end of the section. That relay once more responds and causes the track rails I and 2 again to be sup plied with code step pulses of auxiliary energy. These in turn are transmitted to the detector relay KR. at the exit location E and in responding to them the contact I5 thereof once more recurrently completes the energizing circuit for the approach relay AR. That relay again picks up and due to its slow release characteristics continuously deenergizes the wayside signal Se and the track transformer TT at location E, thereby restoring both of these devices to their normally inactive state.

From the standpoint of operation the facilities of Fig. 4 are the full equivalent of those shown at location E in Fig. l. Both function to prolong each period of pick-up of the code following detector relay KR for the full duration of the signal code off period Within which the pick-up action occurs and they thus permit the release period of the approach relay AR to be reduced to the extent that the approach relay may respond to a shunting of the track circuit with a quickness sufficient to avoid cab signal flips at block joints.

Each of the embodiments of my invention so far described incorporates means for obtaining very nearly equal on and orf periods (when the signal control codes produced by device CR have equal on and off times) of energization for the slow release approach relay AR When controlled by the code following detector relay AR in response to code step pulses of auxiliary energy received from the trackway. This substantial equality of on and olf periods is maintained, moreover, over a Wide range of code speeds even though the duration of the auxiliary energy pulses may be the same for all of the several codes. In that event, of course, the duration of the auxiliary energy pulse is the same for each operation of the impulse relay IR at the entrance end of location D but occurs at diiferent intervals in accordance with the spacing of the energy pulses of the main signal control code supplied to the rails at the exit end location E over the continuously operating Contact 5 of the coding device CR.

In addition to obtaining the on time correction feature in the detector relay KR, I am able definitely to detect the absence of an auxiliary energy pulse in a single code cycle and I obtain this detection by further application of the basic stick circuit arrangement disclosed in Figs. 1, 2 and 4 for the code following detector relay KR. Circuits showing various means for detecting an omission of the auxiliary pulse within one code cycle are shown in each of Figs. 5 to 9 inclusive.

The desirability of such detection is to provide further assurance against the giving of undesirable cab signal flips at block joints. Generally speaking, it is desirable that the detection be quickened at the higher code speeds. Moreover, the less time required to introduce the new codes as the train rst enters each track circuit, the less chance there will be for a cab signal flip to occur. In all events, it is desirable to detect the entry of a train into the track section within one code cycle, since this positively assures that the higher the signal control code the lower the detecting time will be. For example, in the case of the pulse per minute code represented in Fig. 3 the maximum detecting time will be S/lo second (the code cycle length) and for the previously described pulse per minute code the maximum time Will be reduced to the smaller code cycle length of 3V100 second.

' Referring to Fig. 5, I have there represented exit end facilities for an approach control without line wire scheme of the general character described in connection with track section D-E of Fig. 1. These facilities cooperate with the constantly operating coding device CR which is arranged repeatedly to connect the track rails I and 2 of the section to the rear of location E first with the track battery TB and then with the pick-up winding I1 of the code following detector relay KR2. The arrangement of coding contact of device CR differs from that shown in Fig. 1 in that the track battery connection is established when the contact is in its lowermost position and the relay winding is established when the contact is in its uppermost position. The two arrangements are, however, interchangeable and hence either may be used. In the case of both the coding device CR operates continuously under ordinary conditions.

The detector relay KRZ is represented as being a duplicate of the correspondingly designated device of Fig. l. It is provided with a separate stick winding I8 which following each response of the relay is supplied with energizing current over front contact I6 of relay KR2 and iront contact I9 of coding device CR. This stick circuit is interrupted at contact I9 at the end of each off period of the signal control code from battery TB.

The slow release approach relay shown at ARI in Fig. 5 also may be a duplicate oi the device AR of Fig. 1 with the exception that the period of its release delay need not be as great. Its energizing circuit is completed over front contact I5Vof detector relay KRZ in the same manner as in Fig. 2. In addition, the relay ARI is provided with a supplementary yenergizing circuit which is Set up by a front contact 50 of the relay and which is completed over a conductor 5I each time that the contact I9 of the coding device CR occupies the lowermost or on period position of the main signal control code. As in Fig. 1, this approach relay AR is provided with contacts 9 and II' which respectively control the wayside signal Se and the connection of transformer T'I at location E with the alternating current source B--C.

Whereas in the schemes of Figs. l, 2 and 4 the approach relay AR must be designed with a release delay period sufficient to span the spacing between consecutive pick-ups of contact I5 of the detector relay KR2, in the arrangement of Fig. 5 a much smaller period of release delay is adequate due to the supplementary energization supplied over back contact I9 of the coding device CR and front contact 50 of the relay AR. The length of this reduced delay need only be sufficient to span the time required for contact I9 of device CR lto move from the lowermost to the uppermost position plus that for detector relay KRZ to pick up contact I6 in response to a pulse of auxiliary energy received from the track rails. The absolute magnitude of the named period is comparatively small and does not materially change for different rates of signal control code which contact 5 of device CR produces.

For the purpose of assuring quick response of the approach relay AR it is desirable to limit its release delay period to a value only sufficiently greater than that just stated to assure that the relay will not flip, For approach control systems of the type now under consideration a release delay value of the lorder of 1% second will ordinarily be adequate. This, it will be noted, is substantially less than the 33/100 second cycle length for the 180' pulse per minute code previously referred to.

In explaining the operation of the approach control facilities of Fig. 5, assume that the rails I and 2 extending rearwardly from the exit location E are connected with entrance end facilities of the character represented at location D in Fig. 1. Under all traic conditions of the track section D-E, device CR of Fig. 5 continuously operates its contacts. Contact 5 thus repeatedly connects the rails I and 2 rst with the track battery TB and then with the pickup winding I1 of the detector relay KR2 and contact I9 likewise repeatedly connects the plus power source terminal first with the approach relay circuit conductor 5I and then with the detector relay stick circuit.

As long as the section remains vacant the track battery 'IB at location E thus supplies the operating winding of the track relay TR at location D with recurring pulses of pick-up energy. The winding supply circuit which is eiective during each on period of this direct current trackway code may be traced from the positive terminal of the track battery rthrough current limiting impedance 22, back contact 5 of device CR, conductor 23, track rail I,l conductor 24, (see Fig. l), the winding of relay TR, conductor 25, back contact I3 of relay IR, conductor 26, track rail 2, (see Fig. 5), conductor 21 and the secondary of transformer TT back `to the. negative terminal of the track battery TB.

In this manner the track relay TR is caused to pick up its contacts upon the occasion and for the duration of each of the on periods of the signal control code. During the off periods which intervene it releases in the manner alreadyexplained in the description of Fig. 1 and causes the impulse relay IR momentarily to connect the auxiliary battery AB in energy supplying relation with the rails I and 2. These rails transmit a pulse of pick-up energy to the winding I1 of the detector relay KR2 at location E. The winding supply circuit now effective may be traced from the positive terminal of battery AB at location D (see Fig. 1) through impedance 35, iront contact I3 of relay IR, conductor 26, the track rail 2, conductor 21, (see Fig, 5), the pickup winding I1 of relay KRZ at location E, conductor 36, front contact 5 of device CR, conductor 23, track rail I, conductor 24 (Fig. 1), and conductor 31 back to the negative terminal of the battery AB.

As long as the track section D-E remains vacant the pick-up winding of detector relay KR2 is in this manner supplied with the recurring code step pulses of auxiliary energy from battery AB. In responding to each of these pulses, it completes at contact I5 an energizing circuit for the Slow release approach relay AR, which circuit may be traced from the positive terminal of a suitable supply source through front contact Ii of relay KRZ, conductor 4I, and the winding of relay AR back to the negative terminal of the supply source.

In the arrangement of Fig. 5, these recurring code step pulses of energy for relay AR are supplemented by interposed energizing pulses supplied over the second circuit before described as including conductor 5I. This circuit is set up by front contact 50 of relay AR when picked up, and is completed each time that contact I9 of codingvdeviceCRoccupies the lowermost or on period position for the signal control code from battery TB. This supplementary circuitmay be traced from the positive terminal of .a suitable supply source through back contact I9 of device CR, conductor 5I, front contact 50 of relay AR, conductor 53 and the winding of relay AR back to the negative terminal of the supply source.

Due to its slow releasing characteristics which are suiiicient to bridge the longest interval between recurrent pulses of energization supplied over the two circuits just described, the approach relay AR holds its contacts 9 and I I continuously picked up under the stated conditions and thereby renders inactive the wayside signal Se and the cab signal supplycircuit involving source B-C.

Inthe event .that a train comes into the track section at the rear of location E, the usual shunting action of its wheels and axles continuously deenergizes the operating winding of relay TR (see Fig. l) and causes that relay to stay released. The presence of the train within the section also cuts olf the supply of auxiliary energy to the picklup winding I7 of detector relay KR2. That relay also stays continuously released and the supply of recurring pulses of energy to the winding of the slow release approach relay AR over contact I5 is accordingly discontinued.

Even though this approach relay AR should receive (which it ordinarily will not) one or more interposed energizing pulses over Contact I9 of coding device CR during the on period of the trackway code cycle which follows, it will not remain picked up because such succeeding interposed pulses are more widely spaced than the interval of release delay for which relay AR is designed. Not being able to span the interval Vbetween consecutive released positions of coding device contact I9, the approach relay AR releases and breaks the second energizing circuit at contact 50 before the succeeding on code period occurs. Contact 9 of relay AR now completes a lighting circuit for the active lamp at the wayside signal Se and` companion contact II connects the track transformer TT with the cab signal source B-C. The primary supply circuit now completed for the transformer is a duplicate of that shown in Fig. 4.

Each time, now, that coding contact 5 occupies the lowermost position the secondary winding of the transformer TT supplies alternating current energy to the track rails over a circuit which may be traced from the upper terminal of the transformer secondary through the track battery TB, impedance 22, coding contact 5, conductor 23, the track rail I, the train Awheels and axles (not shown), rail 2, and the conductor 21 back to the lower terminal of the transformer secondary. This coded alternating energy is effective for controlling train carried cab signals.

When the rear of the departing train clears the exit end location E the rails I and 2 again transmit coded direct current energy from battery TB to the track relay TR at the entrance location D (Fig. 1). That relay resumes its code following response, code step pulses of auxiliary energy of battery AB are again supplied to the rails and by them transmitted to the detector relay KR2, that relay resumes its code following response, the approach relay AR is once more picked up, and the approach controlled signalling functions are by it restored to their normally inactive state in which they continue until track section D-E once becomes occupied.

From the foregoing it will be seen that the facilities of Fig.A 5 are effective to `detect the absence of received auxiliary energy within the spaceV of asingle code cycle. This is because the approach relay ARI requires that energizing pulses alternatel'y be supplied over contact I5 of relay KRZ and Contact I9 of coding device CR to maintain its-contacts in the picked-up position. As has been explained, the absence of a single one of either of the two types of pulses produces a gapgreater than the release delay period for the relay AR and thus causes it to release. In this manner the response of the relay to a shunting of the track circuit is so quickened that cab signal flips at block joints are effectively prevented at all times.

Referring now to Fig. 6, I have represented a modified form of exit end apparatus which also produces the result just stated. In many respects it is identical with the arrangement of Fig. 5 and differs therefrom chiefly in utilizing a code following detector relay KR3 which has a slight delay in its release and also in using an added relay KA for aiding this detector relay in controlling the approach relay ARI. This added relay KA is provided with a pick-up circuit which includes back contact I9 of coding device AR and a front contact 55 of relay KR3 and with a stick circuit which includes the same back Contact I9 and a front contact 56 of device KA. This added relayKA, moreover, is provided with a control contact 51 which is connected in parallel with the detector relay contact `I5 in the energizing circuit forthe approach relay ARI.

That relay ARI may be a duplicate of the correspondingly identified device shown in the system of Fig. 5. It has a release delay period of the reduced order already described in connection with that earlier figure and is provided with contacts 9 and II which, through circuits not reproduced in Fig. 6, control the energization of the wayside signal Se and the facilities for supplying coded cab signal control energy to the rear track circuit.

From the track rails I and 2 down to and including the stick circuit (shown as including conductor 58) of the detector relay KR3, the apparatus of Fig. 6 is substantially a duplicate of that shown in Fig. 5. Up to this point the Fig. 6 equipment operates in the same manner as does the Fig. 5 apparatus. That is, each pulse of auxiliary energy received from the rails picks up relay KR3 and completes at contact I5 the energizing circuit for the approach relay ARI. The action of the added relay KA, however, is distinctive and will now be described.

This added relay KA is a code following device. Each time that detector relay KR3 is picked up by a pulse of auxiliary energy received from the trackway it completes its own stick circuit at contact I6. This circuit may be traced from the positive lterminal of a suitable supply source through front contact I9 of the coding relay CR, front contact I6 of relay KR3, conductor 58, and the stick winding I8 of the detector relay back to the negative terminal of the supply source. As in the case of the earlier described figures, the effect of thestick circuit is to maintain the relay KR3 picked up until the end of the off period of the signal control code within which that pickup occurs.

As already mentioned, the detector relay KR3 of Fig. 6 is made slightly slow in releasing in order that coding device contact I9 may return to the lowermost or on code position before contact 55 of relay KR3 drops out. Under this condition, the added relay KA is Ipickedfupy over a circuit which extends from the positive supply terminal through back contact I9 of relay CR, conductor 60, front contact 55 of relay KR3, conductor 6I, and the winding of relay KA back to the negative supply terminal.

Once picked up, relay KA locks itself in over its before referred to stick circuit which may be traced from the positive supply terminal through back contact I9 of device CR, conductor 62, front contact 56 of relay KA, conductor 6I and the winding of relay KA back to the negative supply terminal. This stick circuit remains completed until the end of the on code period at which time contact I9 of device CR moves upwardly and breaks the circuit, thereby allowing the added relay KA to release. y

In the manner just explained, relay KA picks up at the beginning of each of the on code periods produced by device CR and releases at the end of the period. Contact 5l of device KA is thus caused to complete for the slow release relay ARI its supplementary energizing circuit which may be traced from the positive terminal of a suitable supply source through front contact 5l of relay KA, conductor 4I and the Winding of relay ARI back to the negative supply terminal.

From the foregoing it will be seen that as long as the track section to the rear of location E remains vacant the apparatus of Fig. 6 is effective to supply relay ARI with a pulse of pick-up energization during each of the off code periods produced by device CR and also with a pulse of supplemental or hold-up energization during each of the on periods of that code. In this manner the relay ARI is enabled to hold its contacts 9 and II continuously picked up when the release period for this relay is reduced to the comparatively low value already described.

In the event that a train comes into the track section to the rear of location E, the code following operation of the detector relay KR3 immediately ceases, the energizing pulse normally supplied to the approach relay ARI over contact I5 is omitted during the iirst cycle of the signal control code which follows entry of the train into the section and the relay ARI accordingly releases because its delay release period is insuicient to bridge the time until the next on vperiod of the code occurs.

Referring to Fig. 7, I have there shown a still further modied form of apparatus for detecting the absence of received auxiliary energy within the space of a single code cycle. The representation of Fig. 7is only partial'and in considering it it will be appreciated that it is intended for use with the complete exit end facilities which are shown in Figs. 5 and 6 and which cooperate with entrance end facilities of the character represented at location D in Fig. 1.

As in the system of Fig. 6, use is made of an added relay KAI. This may be a duplicate of the relay KA of Fig. 6 with the exception that it is, arranged to have slow releasing characteristics. The code following detector relay KR3 of Fig. 7 is made slightly slow releasing as in the system of Fig. 6. Similarly, the approach relay ARI has a comparatively short release delay period and in other respects may be a duplicate of the correspondingly identified device of Figs. 5 and 6.

In operation of the equipment of Fig. 7, each response by the detector relay KR3 to a pulse of auxiliary energy received from the track rails relay ARI an energizing circuit which is a duplicate of that shown in Fig. 6 and which may be traced from the positive terminal of a suitable supply source through conductor 64, front contact I5 of relay KR3, conductor 4I and the winding of relay ARI back to the negative terminal of the supply source. At the same time contact I6 completes for the detector relay KR3 a stick circuit which may be traced from the positive supply terminal through front contact I6, conductor 39, front contact I9 of the coding device CR and the stick Winding I3 of the relay back to the negative supply terminal.

In this manner, the winding of the approach relay ARI is supplied with a pulse of energy during the full continuance of each of the off periods of the main signal control code which device CR produces.

Each time that the contacts of this device CR are in the lowermost or on code period positions, the added relay KAI is picked up over a circuit which may be traced from the positive terminal of a suitable supply source through front contact I6 of `detector relay KR3, conductor 39, back contact I9 of device CR, conductor 6I and the winding of relay KAI back to the negative terminal of the supply source. 'Ihe circuit just traced is completed at the beginning of each of the on code periods mentioned and it continues until the period of release delay for relay KR3 has expired.

Each time that relay KAI is thus picked up, contact 51 thereof completes for the winding of the approach relay ARI an energizing circuit which is the same as that traced during the description of Fig. 6. This circuit remains cornpleted for the full duration of the release delay period of the added relay KAI. Preferably this delay is so chosen that the circuit is interrupted only just before the end of each of the on periods of the highest speed code which the signailing system employs.

From the foregoing it will be seen that under conditions of track section vacancy the apparatus of Fig. 7 operates to .supply the approach rel-ay ARI with a separate pulse of energizing current during each of the on, periods and during each of the olf periods of the signal control code which device CR produces. In consequence, relay ARI is enabled to hold up its contacts 9 and II continuously picked up even though the period of its release delay is of a comparatively low order.

Upon entry of a train into the track section with the rails of which conductors 23 and 21 of Fig. '7 are connected, the detector relay KR3 immediately ceases its code following operation, contact I5 thereof causes a pulse of energy for relay ARI to be omitted during the off period of the first cycle of code which occurs following the entry of the train into the section, and relay ARI releases its contacts before ythe next on code period occurs. In this manner the absence of received auxiliary energy is detected within the space of a single code cycle.

Referring to Fig. 8, I have there represented a still further modified form of apparatus for achieving the result just stated. There, use is made of an added relay KAZ which is provided with separate pick-up and stick windings 66 and 61. 'I'his relay may be of the quick releasing code following type. Use also is made of a code following detecting relay KR3 which has release delay characteristics of the small order explain-ed in connection with Figs. 6 and 7. The approach relay ARI is controlled in a manner identical 75 with that explained in connection with these same figures and it preferably has delay release characteristics of the comparatively low order previously described.

In operation of the apparatus of Fig. 8, each time that the detector relay KR3 responds to a pulse of auxiliary energy received over conductors E3 and 2l from the track rails (not shown), contact I6 completes the relay stick circuit and thus insures that the pick-up condition will be maintained until the endof the o code period. At the same time, contact I5 completes the before traced energizing circuit for the slow release approach relay ARI.

At the beginning of the succeeding on period in the code produced by device CR, contact IS of that device picks up the added relay KA2 over a circuit which may be traced from the positive supply terminal through front contact I6 of relay KR3, conductor`39, back contact I9 of device CR, conductor B I, and the pick-up winding 55 of relay KA2 back to the negative supply termin-al.

As in the case of Fig. '7, relay KR3 is provided with release delay characteristics which enable Vit to remain picked up for a short time following the beginning of each on code period. At the beginning of ea-ch of these on periods moreover, contact 68 of the device CR completes for the relay KA2 a stick circuit which may be traced from the positive terminal of a suitable supply source through -a front contact 69 of the relay KAE, conductor 1B, back contact 68 of relay CR, conductor 'Il and the stick winding 67 of relay KAZ back to the negative supply terminal.

This stick circuit holds relay KA2 picked up during the full continuance of each of the on periods of the trackway codes produced by device CR. As a result contact 51 of relay KA2 causes the winding of the approach relay ARI to be supplied with energizing current during each of these on periods over a circuit previously traced connection with Figs. 6 and '7 as including conductor l I.

From the foregoing it will be seen that during vacant conditions of the track section the apparatus of Fig. 8 functions to supply the approach relay ARI with 4energizing current during each of the on and the off periods of the m-ain signal control code which device CR produces. In this manner the approach relay is enabled to hold its contacts 9 and Il continuously picked up even though the period of its release delay is of the comparatively low order already described.

In the event that a train enters the section to the rails of which conductors 23 and 2l of Fig. 8 are connected, the detector relay KR3 immediately ceases its code following response and Contact I5 thereof causes the pulse of energy normally supplied to the approach relay ARI to be omitted during the rst off period of the code cycle which follows the entry of the train into the section. Because of its short period release delay, the relay ARI now drops out and in this manner the absence of received auxiliary energy is detected within the space of a single code cycle.

Referring nally to Fig. 9, the equipment there represented is also capable of producing the result just stated. It is similar to the apparatus of the immediately preceding figures and differs therefrom chiefly in its employment of an approach relay AR2 which is provided with two separate windings 'I3 and 1li. At proper times the first of these windings receives energizing current over a circuit which includes back contact I9 of the coding device CR and one or the other of the contacts I5 and 5'! of devices KR3 and KA. At other proper times the second winding of the approach relay is energized over iront contact I9 of coding device CR and front contact Il of detector relay KR3.

Aside from having the two separate windings the approach relay AR2 is similar to the device ARI of the earlier described gures in that it is provided with a comparatively short period of contact release delay. The code following detector relay KR3 may be a duplicate of that of the correspondingly identified device of the earlier gures. The added relay KA is a quick releasing code following device which may correspond to the relay KA of Fig. 6.

In operation of the equipment of Fig. 9, each time that the detector relay KR3 responds to a pulse of aruxiliary energy received from the trackway, contact I6 thereof completes its own stick circuit (represented as including a conductor 89) and thereby assures that relay will remain picked up for the full continuance of the olf code period. At the same time contact I5 of relay KR3 sets up for the winding 'I3 of the approach relay ARZ an energizing circuit which is completed by Contact I9 of device CR at the beginning of the following on code period and which when so completed may be traced from the positive terminal of a suitable supply source though back contact I9, conductor 79, front contact I5 of relay KR3, conductor Il and the winding I3 of relay AR2 back to the negative terminal of the supply source. As in the case of the earlier described gures, relay KR3 is provided with a small amount of release delay in order that the circuit just traced may be completed in the manner described.

In this manner the approach relay ARZ is supplied with an energizing pulse at the beginning of each of the off periods of the main signal control code. Coincident with each of these pulses the added relay KA is picked up over a circuit which may be traced from the positive supply terminal through back contact I9 of device CR, conductor I9, front contact I5 of detector relay KR3, conductors 'I'I and 'I8 and the winding of relay KA back to the negative supply terminal.

In picking up, Contact 51 of relay KA completes for the winding 'I3 of the approach relay AR2 a supplementary energizing circuit which extends from the positive supply terminal through back contact I9 of device CR, conductor 16, front contact 51 of relay KA, conductors 'I8 and 11 and the winding I3 of relay AR2 back to the negative supply terminal. The added relay KA continues to remain energized and hence picked up for the full duration of the on code period and in consequence Contact 51 thereof maintains the just traced auxiliary energizing circuit for the approach relay ARZ completed until the end of the on code period.

Each time that relay KR3 eiects the already described response to a pulse of auxiliary energy and picks up contact I6, there is completed for the second winding 'I4 of the approach relay AR2 an energizing circuit which may be traced from the positive supply terminal through front contact I9 of coding device CR, front contact I6 of relay KR3, conductor 'I9 and the winding 'I4 of relay ARZ back to the negative supply terminal. Once completed this circuit continues active for the full continuance of the off code 75 period and is interrupted only when contact I9 of coding device CR moves to the lowermost position to effect the beginning lof the succeeding on period.

From the foregoing it will be seen that vthe equipment of Fig. 9 functions during conditions of track section vacancy to supply the approach relay AR2 with a pulse of energizing current during each of the on periods and during each of the off periods ofthe signal control code which coding device CR produces. Each of these energizing pulses, moreover, continues for4 the full duration of the particular code period within which it occurs and in this manner the approach relay AR2 is enabled to hold its contacts 9 and Il continuously picked up even though the release delay period'of the relay is exceedingly small.

In the event that a train comes into the track section with the rails of which conductors 23` and 21 of Fig. 9 are connected, the detector relay KR3 immediately discontinues its code following response and contacts l5 and It thereof occupy the lowermost position continuously. This causes winding 'i4 of the approach relay ARZ to remain continuously deenergized. Moreover, the winding 'i3 of relay ARZ likewise is continuously deenergized for the reason that the pick-up circuit for the added relay KA is interrupted at contact l5 and hence contact 51 is released. In consequence, the relay ARZ immediately releases contacts 9 and ll and does this within the space of the first code cycle which follows the entry of the train into the track section.

From the foregoing it will be seen that I have made important improvements in that form of approach control without line wire scheme wherein the rails of each signal block length track transmit code step pulses of auxiliary energy forwardly from the block entrance to effect the energization of a slow release approach relay at the block exit as long as the block remains vacant.

In particular I have provided improved means for detecting these pulses at the exit end of each track circuit and for energizing the associated slow release approach delay in step with them;v I have prolonged each period of this relay energization for the full duration of the signal code off period with which it coincides; Ihave so `quickened the response of the approach relay to auxiliary energy within the space of a single code cycle; and I have accomplished all of the above through the use. of circuit means of compara' tively simple character.

As all of these improvements are entirely a function of the track circuit and apparatus which is directly associated therewith, they are vindependent of the coding and decoding facilities o-f the coded signaling system and hence are usable with a wide variety of different types and vforms 0f such facilities.

embodying my invention, it is understood that Various changes and modifications may be made therein Within the scope of the appended claims without departing from the spirit and scope of my invention.

l I-Iaving thus described my invention, what I claim is:

1. In combination with a section of track, means including a coding device at the section exit for supplying the rails of said section with coded signal control energy consisting of alternate on and olf periods, means effective under vacant conditions of said section foi` further supplying said `rails with a momentary pulse of auxiliary energy during each of said off code periods, a code following detector relay at the section exit provided with a pick-up circuit and with a stick circuit, means controlled by said coding device for connecting said pick-up circuit in energy receiving relation with said rails during said recurrent off code periods whereby as long as said track section remains vacant said detector relay receives said auxiliary energy pulses from those rails and is recurrently picked up thereby, means controlled by said coding device and by said detector relay for completing said stick circuit from the time of each pick-up of the detector relay until the end of the off code period withinwhich that pick-up occurs whereby to prolong the hold-up time of that relay for the full duration of each of those off code periods, a` slow release approach relay energized in step with the said recurrent pick-ups of said detector relay whereby to be maintained continuously picked up as long as said section is vacant and to release only when a train comes into the section, and traiiic governing apparatus controlled by said approach relay.

2. In a railway signaling system which includes a section of track, the combination of means including a coding device at the section exit for supplying the rails of said section with track circuit energy in the form of alternate on and off periods that recur rapidly at times to constitute a fast code and more slowly at other times to constitute a slow code, means effective at the beginning of each off period of the said coded energy which is received from said rails for further supplying those rails with a pulse of auxiliary energy of an unvarying length iixed at less than the off period length of said fast code, a code following detector relay located atthe section exit and provided with a pick-up circuit and with a stick circuit, means controlled by said coding device for connecting said pick-up circuit in energy receiving relation with said rails during said off code periods whereby as long as said track section remains vacant said detector relay receives said auxiliary energy pulses from those rails and is recurrently picked up thereby, means controlled by said coding device and by said detector relay for completing said stick circuit from the time of each pick-up of the detector relay until the .end of the off code period within which that pick-up occurs whereby to prolong the hold-up time of that relay for the full duration of each of lthose off periods, a slow release approach relay energized in step With the said recurrent pick-ups of said detector relay whereby to be maintained continuously picked up as long as said section is unoccupied, and traflc governing apparatus controlled by said approach relay and rendered active when that relay releases in response to the presence of a train in said section.

Inl combination, a section of railway track,

sofL

means including a coding device at the section exit for supplying the rails of said section with track circuit energy in the form of alternate on and off periods that recur rapidly at times to constitute a fast code and more slowly at other times to constitute a slow code, a code following track relay connected with said rails and operated by the said coded energy which is received therefrom, means controlled by said track relay and effective at the beginning of each oi period of the received track circuit code to supply said rails with a pulse of auxiliary energy of an unvarying length xed at less than the off period length of said fast code, a code following detector relay at the section exit provided with a pick-up circuit and with a stick circuit, means controlled by said coding device for connecting said pick-up circuit in energy receiving relation with the section rails during each of the said off code periods whereby as long as said track section remains vacant said detector relay receives said auxiliary energy pulses from those rails and is recurrently picked up thereby, means controlled by said coding device and by said detector relay for completing said stick sircuit from the time of each pick-up of the detector relay until the end of the off code period within which that pick-up occurs whereby to prolong the hold-up time of that relay for the full duration of each of those oil periods, a slow release approach relay energized in step with the said recurrent pick-ups of said detector relay whereby to be maintained continuously picked up as long as said section is :vacant and to release only when a train comes into the section, and traflic governing apparatus controlled by said approach relay.

4. In combination, a section of railway track, a source of trackway energy for the rails of said section, a continuously operating coding device at the section exit which includes a coding contact, means including said contact for recurrently connecting said source to said rails whereby to produce a trackway code consistingk of alternate on and off periods, means effective under vacant conditions of said section for further supplying a momentary pulse of auxiliary energy to said rails during each of said off code periods, a code following detector relay installed at the section exit and provided with a pick-up circuit and with a stick circuit, means including the aforesaid coding contact for connecting said pick-up circuit in energy receiving relation with said rails during each of said 01T code periods whereby as long as said track section remains vacant said detector relay receives and is recurrently picked up by said auxiliary energy, means controlled by said coding device and by said detector relay for completing said stick circuit from the time of each pick-up of the detector relay until the end of the 01T code period within which that pick-up loccurs whereby to prolong the hold-up time of that relay for the full duration of each of those off periods, a slow release approach relay, means controlled by said detector relay for energizing said approach relay in step with the said recurrent pick-ups of the detector relay whereby to maintain the approach relay continuously picked up as long as said section is vacant and to allow that relay to release only when a train comes into the section, and traffic governing apparatus controlled by said approach relay.

5. In combination with a section of railway track, a source of trackway energy and a code following detector relay at the section exit, a continuously operating coding contact which repeatedly connects the rails of said section rst to said trackway energy source and then to the winding of said detector relay and thereby produces a trackway code consisting of alternate on and off periods the latter of which coincide with said relay winding connections, a code following track relay connected with said rails and operated by the said coded energy which is received therefrom, means controlled by said track relay for supplying auxiliary energy to said rails during each of the said ofi periods of the said received trackway code whereby as long as said track section remains vacant said detector relay receives said auxiliary energy from those rails and is recurrently picked up thereby, a slow release approach relay, means controlled by said detector relay for energizing said approach relay in step with the said recurrent pick-ups of the detector relay whereby to maintain the approach relay continuously picked up under vacant conditions of said section and to allow that relay to release only when said section becomes occupied, and traic governing apparatus controlled by said approach relay.

6. In combination with a section of track which forms a part of a railway signaling system of the coded track circuit class, approach control facilities comprising a source of track circuit energy at the exit end of the section, a code following detector relay also located at the section exit and provided with a pick-up circuit and with a stick circuit, a similarly located coding device having a contact which repeatedly connects the rails of said section rst to said trackway energy source and then to said pick-up circuit and thereby produces a trackway code consisting of alternate on and off periods the latter of which coincide with said pick-up circuit connections, a code following track relay connected with said rails and operated by the said coded energy which is received therefrom, a source of auxiliary energy, means controlled by said track relay for momentarily connecting said rails to said auxiliary source each time that the track relay releases whereby during each of the said off periods of the received trackway code those rails receive a short pulse of auxiliary energy which they transmit forwardly to the said pick-up circuit of said detector relay and thereby cause that relay recurrently to pick up as long as said section remains vacant, a local source of stick energy for the detector relay, means controlled by said coding device and by said detector relay for connecting said local source to the said stick circuit of the detector relay from the time of each pick-up of that relay until the end of the off cod-e period within which that pick-up occurs whereby to prolong the hold-up time of the detector relay for the full duration of each of those 01T periods, a slow release approach relay, means controlled by said detector relay for energizing said approach relay in step with the responses of the detector relay whereby to maintain the approach relay continuously picked upy as long as said section is vacant and to allow that relay to release only when a train comes into the section, and traffic governing apparatus controlled b said approach relay.

7. In combination with a section of railway track, means including a coding device at the section exit for supplying the section rails with signal control energy in the form of alternate on and off periods that recur rapidly at times to constitute a fast code and more slowly at other times to constitute a slow code, a code following detector relay also at the section exit provided with a pick-up circuit and with a stick circuit, means including a contact of said coding device for connecting said pick-up circuit in lenergy receiving relation with said rails during each of the said oli code periods, means effective at the beginning of each ofi period of the said coded energywhich is received from said rails forv further supplying those rails with a pulse of auxiliary energy of an unvarying length Xed at less than the"ofi period length of said fast code whereby recurrently to excite the said pick-up circuit of said detector relay and thereby cause that relay recurrently to pick up as long as said section remains vacant, means controlled by said coding device and b-y said detector relay for completing the saidv stick circuit of the `detector relay from the time of each pick-up of that relay until the end oi the off code period within which that pick-up'occurs whereby to prolong the hold-up time of the detector relay for the full duration of each of those off periods, a slow release approach relay energized in step with the said recurrent pick-ups of said detector relay whereby to be maintained continuously picked up as long as said section is vacant and to release only when a train comes into the section, and traffic governing apparatus controlled by said approach relay.

8. In combination with a section of 'railway track, a source o-f'trackway energy at the section exit, a code following detector relay also located at the section exit and provided with a pick-up circuit and with a stick circuit, a similarly located coding device having a contact which repeatedly connects the rails of said track section iirst to said Venergy source and then to said relay pick-up circuit and thereby produces a trackway code consisting of alternate on and oi periods the latter of which coincide with said pick-up circuit connections, means for further supplying said rails with auxiliary energy whereby momentarily to excite the said pick-'up circuit of said detector relay at the beginning of' each of said oil code periods andthereby cause that relay recurrently to pick up'as long as said section remains-vacant, means controlled by said coding device and by-said 'detector relay for completing said relay stick circuit from the time of each pick-up of the detector relay until the end of the said off code period within which that pick-up occurs whereby to prolong the hold-up time of that relay for the full duration of each of those off periods, a slow release approach relay, means controlled by said detector relay for energizing said approach relay in step with the said recurrent pick-ups of the detector relay whereby to maintain the approach relay continuously picked up as long as said section is vacant and to allow that relay to release only when a train comes into the section, and traiiic governing apparatus controlled by said approach relay.

' 9. In combination with a section of railway track, means including a coding device at the section exit for supplying the rails of said section with coded signal control energy consisting of alternate on and off periods, a code .following detector relay also located at the section exit and provided with a pick-up circuit and with a stick circuit, means including a contact of said coding device for connecting said lpick-wup circuit across said rails during each of said-ofi code periods,

means controlled by the said coded energy which is received from said rails for further supplying those rails with a pulse of auxiliary energy of momentary length at the beginning of each oli period of the received code whereby recurrently to excite the said pick-up circuit of said detector relay and thereby cause that relay recurrently to pick up as long as said section remains vacant, a source of stick energy, means including a front contact of said detector relay and a contact of said coding device that is closed during the 01T periods of said signal control code for connecting the said stick circuit of said detector relay to said stick energy source from the time of each pick-up of the detector relay until the end of the said 01T code period within which that pick-up occurs whereby to prolong the hold-up time of that relay for the full duration of each of those ofi periods, a slow release approach relay energized in step with the said recurrent pick-ups of the detector relay whereby to be maintained continuously picked up as long as said section is vacant and to release only when a train comes into the section, and traffic governing apparatus controlled by said approach relay.

10. In combination with a section of railway track, approach control facilities comprising means including a coding device at the section exit for supplying the rails of the section with coded signal control energy consisting of alternate on and 01T periods, a code following detector relay also at the section exit, means controlled by said coding device for connecting the winding of said relay in energy receiving relation with said rails during each of the said off periods of said signal control code and for interrupting that connection during the on periods of that code, means for further supplying said section rails with auxiliary energy whereby to excite said detector relay during said off code periods and thereby cause that relay recurrently to pick up as long as said section remains vacant, a slow release approach relay, means controlled by said detector relay for energizing said approach relay in step with the said recurrent pick-ups of the detector relay whereby to maintain the approach relay continuously picked up under vacant conditions of said section and to allow that relay to release only when said section becomes occupied, and tralilc governing apparatus controlled by said approach relay.

11. In a railway signaling system which includes a section of track, the combination of means including a coding device at the section exit for supplying the rails of said section with coded signal control energy consisting of alternate on and off periods, a code following track relay connected with said rails and operated by the said coded energy which is received therefrom, means controlled by said track relay for supplying said rails with a momentary pulse of auxiliary energy at the beginning of each of the said 01T periods of the received signal control code, a code following detector relay located at the section exit and provided with a pick-up winding and with a stick winding, means controlled by said coding device for connecting said pick-up winding across said rails during each of the said 01T periods of said signal control code whereby as long as said track section remains vacant said detector relay receives said pulses of auxiliary energy from those rails and is recurrently picked up thereby, a source of stick energy, means controlled b-y said coding device and by said detector relay for connecting `said. stick winding to said stick energy source from the time of each pickup of the detector relay until the end of the off code period within which that pick-up occurs whereby to prolong the hold-up time of that relay for the full duration of each of those off periods, a slow release approach relay energized in step with the said recurrent pick-ups of the detector relay whereby to be maintained continuously picked up under vacant conditions of said section and to release only when said section becomes occupied, and traic governing apparatus controlled by said approach relay.

12. In combination with a section of railway track, a source of trackway energy at the section exit, a similarly located code following detector relay having a pick-up winding and a stick winding, a continuously operating coding device also at the section exit, means including a contact of said device for repeatedly connecting the rails of said track section first to said trackway energy source and then to said pick-up winding of the detector relay whereby to produce a trackway code consisting of alternate on and orf periods the latter of which coincide with said pick-up 1, winding connections, means controlled by the said coded energy which is received from said rails for further supplying those rails with a pulse of auxiliary energy of momentary length at the beginning of each off period of the received code whereby to excite said pick-up winding during those olf periods and cause said detector relay recurrently to pick up as long as said section remains vacant, a source of stick energy, means including a Ycontact of said coding device and a contact of said detector relay for connecting the said stick winding of that relay to said stick energy source from the time of each pickup of the detector relay until the end of the said off code period within which that pick-up occurs whereby to prolong the hold-up time of that relay for the full duration of each of those o code periods, a slow release approach relay, means controlled by said detector relay for energizing said approach relay in step with the said recurrent pick-ups of the detector relay whereby to maintain the approach relay continuously picked up under vacant conditions of said section and to allow that relay to release only when said section becomes occupied, and traflc governingV apparatus controlled by said approach relay.

13. In combination with a section of railway track, approach control facilities comprising a source of trackway energy at the section exit, a similarly located code following detector relay provided with a pick-up winding and with a stick winding, a continuously operating coding device also at the section exit, means including a contact of said device for repeatedly connecting the rails of said track section rst to said trackway energy source and then to said relay pick-up winding whereby to produce a trackway code consisting of alternate on and off periods the latter of which coincide with said pick-up winding connections, means for further supplying said rails with auxiliary energy whereby to excite said pick-up winding during said off code periods and thereby cause said detector relay recurrently to pick up as long as said section remains vacant, a source of stick energy, means including a contact of said coding device and a contact of said detector relay for connecting the said stick winding of that relay to said stick energy source from the time of each pick-up of the detector relay until the end of the said off code period within which that pick-up occurs whereby to prolong the holdup time of that relay for the full duration of each of said ofi code periods, a slow release approach relay, means controlled by said detector relay for energizing said approach relay in step with the said recurrent pick-ups of said detector relay whereby to maintain the approach relay continuously picked up under vacant conditions of said section and to allow that relay to release only when said section becomes occupied, and traino governing apparatus controlled by said approach relay.

14. In combination, a section of track, means including a coding device at the section exit for supplying the rails of said section with coded signal control energy consisting of alternate on and off periods, a code following detector relay also located at the section exit and having a pick-up circuit and a stick circuit, means controlled by said coding device for connecting said pick-up circuit in energy receiving relation with said rails during each 01T period of the signal control code, means for further supplying said section rails with auxiliary energy whereby to excite said pick-up circuit during said off code periods and thereby cause said detector relay recurrently to pick up as long as said section remains vacant, means controlled by said coding device and by said detector relay for completing said stick circuit from the time of each pick-up of the detector relay until the end of the said olf code period within which that pick-up occurs whereby to prolong the hold-up time of that relay for the full duration of each said off code periods, a slow release approach relay, means including a transformer excited over a direct current circuit controlled by a contact of said detector relay for energizing the winding of said approach relay in step with the said recurrent pick-ups of the detector relay whereby to maintain the approach relay continuously picked up ..1

as long as said section is vacant and to allow that relay to release only when a train cornes into the section, and trac governing apparatus controlled by said approach relay.

15. In combination, a section of track, means including a coding device at the section exit for supplying the rails of said section with coded signal control energy consisting of alternate on and off periods, a code following detector relay also located at said section exit and having a pick-up circuit and a stick circuit, means controlled by said coding device for connecting said pick-up circuit in energy receiving relation with said rails during each off period of the signal control code, means for further supplying said section rails with auxiliary energy whereby to excite said pick-up circuit during said off code periods and thereby cause said detector relay recurrently to pick up as long as said section remains vacant, means controlled by said coding device and by said detector relay for completing said stick circuit from the time of each pick-up of the detector relay until the end of the said off code period within which that pick-up occurs whereby to prolong the hold-up time of that relay for the full duration of each of said 01T code periods, a slow release approach relay, a circuit completed over a front contact of said detector relay for energizing the winding of said approach relay in step with the said recurrent pick-ups of the detector relay whereby to maintain the approach relay continuously picked up as long as said section is vacant and to allow that relay to release only when a train comes into the section, and trafiic governing apparatus controlled by said approach relay.

16. In combination with a section of railway track, approach control facilities comprising means including a coding device at the section exit for supplying the rails of the section with coded signal control energy consisting of alternate on and oif periods, a code following detector relay also located at the section exit and having a single operating winding, means controlled by said coding device for connecting said relay winding inenergy receiving relation with said rails during each of the said off periods of the said signal control code, means for further supplying the section rails with auxiliary energy whereby to excite said relay winding during said 01T code periods and thereby cause said detector relay recurrently to pick up as long as said section remains vacant, a local source of energy at said section exit, means controlled by said coding device and by said detector relay for connecting said relay winding with said local source from the time of each pick-up of the detector relay until the end of the said off code period within which that pick-up occurs whereby to prolong the hold-up time of that relay for the full duration of each ofA said off code periods, a slow release approach relay, means controlled by said detector relay for energizing said approach relay in step with the said recurrent pick-ups of the detector relay whereby to maintain the approach relay continuously picked up under vacant conditions of said section and to allow thaty relay to release only when said section becomes occupied,

and traffic governing apparatus controlled by said approach relay.

i7. In combination with a section of railway track, approach control facilities comprising a source of trackway energy at the section exit, a similarly located code following detector relay provided with a single operating winding, a continuously operating coding device also at the section exit, means including contacts of said device for connecting the rails of said track section rst to said trackway energy source and then to said relay winding whereby to produce a trackway code consisting of alternate on and off periods the latter of which coincide with said relay winding connections, means for further supplying said rails with auxiliary energy whereby to excite said relay winding during said off code periods and thereby cause said detector relay recurrently to pick up as long as said section remains vacant, a local source of stick energy for said relay, means including a contact of said coding device and a contact of said detector relay for connecting said winding of that relay to said local source from the time of each pick-up of the detector relay until the end of the said foff code period within which that pick-up occurs whereby to prolong the hold-up time of that relay for the full duration of each of said off code periods, a

to release only when said section becomes occupied, and traflic governing apparatus* controlled by said approach relay.

is. In a railway signaling system, the com-v bination with a section of ytrack of` means includingA a coding device atythe section exit for supplying the rails of `said section with coded track circuit energy consisting of alternate on and o periods, a code following track relay connected with said rails and operated by the said coded energy which is received therefrom, means controlled by said track relay for supplylng said rails with a pulse of auxiliary energy during each of the said o periods of the received track circuit code, a code following detector relay at the section exit, means for connecting said detector relay in energy receiving relation with said rails during each of said off code periods whereby as long as said track section remains vacant said detector relay receives said pulses of auxiliary energy from the rails and is recurrently picked up thereby, a slow release approach relay, means controlled by said detector relay for energizing said approach relay in step with the said recurrent pick-ups of the detector relay whereby to maintain the approach relay continuously picked up as long as said section is vacant and to allow that relay to release when and only when a train comes into the section, means for also energizing said approach relay during the said on periods of the signal control code providing said detector relay is receiving and responding to said auxiliary energy during successive off periods of that code whereby to reduce the time of release delay which said approach relay must have in order to stay continuously picked up under said vacant track section conditions, and trafiic governing apparatus controlled by said approach relay.

19. In combination with a section of railway track, approach control facilities comprising means including a coding device at the section exit for supplying the rails of the section with coded signal control energy consisting of alternate on and off periods, a code following detector relay also at `said section exit, means controlled by said coding device for connecting said relay in energy receiving relation with said rails during each of the said o periods of said signal control code, means for further supplying said section rails with auxiliary energy whereby to excite said detector relay during said ofi code periods and thereby cause that relay recurrently to pick up as long as said section remains vacant, a slow release approach relay, a circuit for energizing said approach relay in step with the said ofi period pick-ups of said detector relay whereby to maintain the approach relay continuously picked up as long as said section is vacant and to allow that relay to release only when the section becomes occupied, a circuit for also energizing said approach relay during the said on periods of said signal control code provided said detector relay is receiving and responding to said auxiliary energy during successive off periods of that code whereby to reduce the time of release delay which said approach relay must have in order to stay continuously picked up under said vacant track section conditions, and traffic governing apparatus contro-lled by said approach relay.

20. In combination with a section of railway track, approach control facilities comprising means including a coding'device at the section exit for supplying the rails of the section with coded signal control energy consisting of alternate ,on and off periods, a code following detector relay also located at the section exit and provided with a pick-up circuit and with a stick circuit, means controlled by said coding device for connecting Said pick-up circuit in energy receiving relation with said rails ,during each of the said off periods of said signal control code, means for further supplying the section rails with auxiliary energy whereby to excite said pick-up circuit during said off code periods and thereby cause said detector relay recurrently to pick up as long as said section remains vacant, means controlled by said coding device and by said detector relay for completing said stick circuit from the time of each of said pick-ups of the detector relay until the end of the said off code period within which the pick-up occurs whereby to prolong the hold-up time of that relay for the full duration of each of said oi code periods, a slow release approach relay, means for energizing said approach relay in step with the pickups of said detector relay whereby to maintain the approach relay continuously picked up as long as said section is vacant and to allow that relay to release only when the section becomes occupied, means for also energizing said approach relay during the said on periods of said signal control code provided said detector relay is receiving and responding to said auxiliary energy during successive off periods of that code whereby to reduce the time of release delay which said approach relay must have in order to stay continuously picked up under said vacant track section conditions, and trafc governing apparatus controlled by said approach relay.

2l. In combination with a section of railway track, approach control facilities comprising a source of trackway energy at the section exit, a similarly located code following detector relay, a continuously operating coding device also at the section exit which repeatedly connects the rails of said section first to said trackway energy source and then to the winding of said detector relay and thereby produces a trackway code consisting of alternate on and 01T periods the latter of which coincide .with said relay winding connections, means for further supplying said rails with auxiliary energy whereby to excite said relay winding during said 01T code periods and thereby cause said detector relay recurrently to pick up as long as said section remains vacant, a slow release approach relay, a circuit completed over a front contact of said detector relay for energizing said approach relay each time that the detector relay picks up whereby to maintain the approach relay continuously picked up as long as said section is vacant and to allow that relay to release only when the section becomes occupied, a circuit completed over a front contact of said approach relay and a contact of said coding device for also energizing the approach relay during the said on periods of the trackway code provided said detector relay is recurrently picking up during successive o periods of that code whereby to vreduce the time of release delay which said approach relay must have in order to stay continuously picked up under said vacant track section conditions, and traiiic governing apparatus controlled by said approach relay.

22. In combination with a section of railway track, approach control facilities comprising a Source lof trackway energy at the section exit, a similarly located code following detector relay having a small release delay, a continuously operating coding device at the section exit which repeatedly connects the rails of said section rst to said trackway energy source and then to the winding of said detector relay and thereby produces a trackway code consisting of alternate on and foff periods the latter of which coincide with said relay winding connections, means for further supplying said rails with auxiliary energy whereby to excite said relay winding during said 01T code periods and thereby cause said detector relay recurrently to pick up as long as said section remains Vacant, an added code following relay also at the section exit, a circuit for picking up said added relay over a front contact of said detector relay and a contact of said coding device that is closed during the said on periods of said trackway code, a stick circuit for said added relay which is completed over said coding device contact and a front contact of the added relay, a slow release approach relay, a circuit for energizing said approach relay over a iront contact of either or both of said detector and added relays whereby to maintain the approach relay continuously picked up as long as said section is vacant and to allow that relay to release only when the section becomes occupied, and traiiic governing apparatus controlled by said approach relay.

23. In combination with a section of railway track, approach control facilities comprising a source of trackway energy at the section exit, a similarly located code following detector relay having a slight release delay, a continuously operating coding device at the section exit which repeatedly connects the rails of said section rst to said trackway energy source and then to the winding of said detector relay and thereby produces a trackway code consisting of alternate on and 01T periods the latter of which coincide with said relay winding connections, means for further supplying said rails with auxiliary energy whereby to excite said relay winding during said oifvcode periods and thereby cause said detector relay recurrently to pick up as long as said section remains vacant, an added code following relay also installed at the section exit and also having a small release delay, a circuit for picking up said added relay over a front contact of said detector relay and a contact of said coding device that is closed during the said on periods of said trackway code, a slow release approach relay, a circuit for energizing said approach relay over a front contact of either or both of said detector and added relays whereby to maintain the approach relay continuously picked up as long as said section is vacant and to allow that relay to release only when the section becomes occupied, and traiic governing apparatus controlled by said approach relay.

24. In combination with a section of railway track, approach control facilities comprising a source of trackway energy at the section exit, a similarly located code following detector relay having a small release delay, a continuously operating coding device at the section exit which repeatedly connects the rails of said section rst to said trackway energy source and then to the winding of said detector relay and thereby produces a trackway code consisting of alternate on and off periods the latter of which coincide with said relay winding connections, means for further supplying said rails with auxiliary energy whereby to excite said relay winding during said off code periods and thereby cause said detector relay recurrently to pick up as long as said section remains vacant, an added code following relay also installed at the section exit'and provided with a pick-up winding and with a stick winding, a circuit for energizing said pick-up winding over a front contact of said detector relay and avcontact of said coding device that is closed during the said on periods of said trackway code, a circuit for energizing said stick winding over another contact of said coding device that is closed during said on code periods and a front contact of said added relay, a slow release approach relay, a circuit for energizing said approach relay over a front contact of either or both of said detector and added relays whereby to maintain the approach relay continuously picked up as long as said section is vacant and to allow that relay to release only when the section becomes occupied, and traic governing apparatus controlled by said approach relay.

25. In combination with a section of railway track, approach control facilities comprising a source of trackway energy at the section exit, a similarly located code following detector relay having a small release delay, a continuously operating coding device at the section exit which repeatedly connects the rails of said section first to said trackway energy source and then to the winding of said detector relay and thereby produces a trackway code consisting of alternate on and off periods the latter of which coincide with said relay winding connections, means for further supplying said rails with auxiliary energy whereby to excite said relay winding during said 01T code periods and thereby cause said detector relay recurrently to pick up as long as said section remains vacant, an added code following relay also at the section exit, a circuit for picking up said added relay over a front contact of said detector relay and a contact of said coding device that is closed during said on periods of said trackway code, a stick circuit for said added relay which is completed over Said Coding device contact and a front contact of the added relay, a slow release approach relay provided with two separate windings, a circuit for energizing one of said windings over a contact of said coding device that is closed during said on code periods and a front contact of either or both of said detector and added relays whereby to maintain the approach relay continuously picked up as long as said section is vacant and to allow that relay to release when and only when the section becomes occupied, a circuit for energizing the other of said approach relay windings over a front co-ntact of said detector relay and a contact of said coding device that is closed during the said o periods oi said trackway code whereby to reduce the time of release delay that said approach relay must have in order to stay co-ntinuously picked up under said vacant track section conditions, and trafc governing apparatus controlled by said approach relay.

EDWARD U'. THOMAS. 

